This invention relates to an improved hydraulic brake control assembly for automotive vehicles.
More particularly, this invention relates to an improved hydraulic brake control assembly for automotive vehicles that is responsive to vehicular deceleration and load.
When a driver of an automotive vehicle depresses the brake pedal, a dangerous skidding condition may occur due to the locking of the rear wheels prior to the front wheels. This locking condition generally occurs during certain braking applications and vehicular loads when the same hydraulic brake pressure is applied to both the front and rear wheel brakes from the master brake cylinder of the vehicle. Various devices have been proposed and exist that are positioned between the front or rear wheel brakes, usually the rear wheel brakes, and the master brake cylinder for changing the ratio of the hydraulic pressure on the rear wheel brakes to that of the master brake cylinder pressure.
Generally, it is well-known that vehicle deceleration is proportional to the hydraulic brake pressure and that the hydraulic brake pressure, in order to obtain a certain deceleration, is varied according to the loading conditions of the vehicle, i.e., the brake pressure necessary to obtain a certain deceleration at the minimum vehicle load is smaller than the brake pressure necessary to obtain the same deceleration at the maximum vehicle load. That is to say, as the vehicle load increases the hydraulic pressure necessary for braking must also increase.
It is known to provide a hydraulic brake control device that includes a proportioning valve for changing the hydraulic pressure ratio between the master brake cylinder and rear wheel brakes and a pressure-sensitive valve assembly for regulating and actuating the proportioning valve in accordance with vehicular deceleration.
It is also known to provide the pressure-sensitive valve assembly in such devices with an inertia-responsive member for controlling the admission of the hydraulic pressure to actuate the proportioning valve in accordance with vehicular deceleration. According to the conventional devices, however, the pressure supplied to the pressure-sensitive valve assembly can under certain circumstances be excessive prior to closure of the inertia-responsive member such as when the vehicular driver suddenly depresses the brake pedal during a low vehicular load and produces a sudden hydraulic pressure supplied to the pressure-sensitive assembly from the master cylinder. As a result of this, the large hydraulic pressure applied to the pressure-sensitive assembly causes the proportioning valve to remain unactuated or maintained in its open position and thereby causes application of a large amount of hydraulic pressure to the rear wheel brakes from the master brake cylinder. A serious and undesirable locking condition of the rear wheels can therefore occur during a small vehicular load when using these conventional brake control devices.
In order to prevent this situation, there has been developed a hydraulic brake control assembly of the type described above that uses an orifice in the pressure-sensitive valve assembly to throttle sudden hydraulic pressure from being applied, such as during low vehicular load, and thus provide a proper control of the proportioning valve. Accordingly, when there is low vehicular load and a substantial brake application occurs, the proportioning valve will not remain in its open position but will be actuated or deflected to proportion the hydraulic pressure being applied to the rear wheel brakes from the master brake cylinder to avoid a rear wheel locking condition.
Such a hydraulic brake control assembly is shown in U.S. Pat. No. 3,944,293. However, this hydraulic brake control assembly still does not completely satisfy all vehicular load and braking application conditions to provide the optimum braking force to the wheels. Under certain sudden braking application conditions, hydraulic pressure may not be sufficiently increased because of the throttling effect of the orifice. Consequently, the deflecting or actuation point of the proportioning valve may remain low before closure of the inertia-responsive valve during a large vehicular load such that a sufficient braking force on the rear wheels may not be obtained. This is caused by a premature proportioning of the hydraulic pressure to the rear wheel brakes by the proportioning valve being actuated a low level. In view of the above, it is seen that proper and optimum braking pressure applied to the rear wheel brakes under different vehicular load and braking application conditions has not as yet been achieved by these hydraulic brake control assemblies.
Accordingly, it is a primary object of this invention to provide a new and improved hydraulic brake control assembly which overcomes the aforesaid drawbacks and difficulties in providing a proper and optimum hydraulic braking pressure to the rear and front wheels.
It is a further object of this invention to provide a new and improved hydraulic brake control device which secures a proper hydralic braking pressure under all vehicular load and braking application conditions.
Another object of the invention is to provide a new and improved hydraulic brake control assembly wherein the deflecting or actuation point of the proportioning valve be properly modified in accordance with vehicular deceleration and load, and braking applications.
Still another object of this invention is to provide a new and improved hydraulic brake control assembly which provides a higher deflecting or actuation point of the proportioning valve when braking application is suddenly applied during a high vehicular load.
A further object of this invention is to provide an improved hydraulic braking control assembly which provides the above objects and a low deflecting or actuation point of the proportioning valve when braking application is suddenly applied during a low vehicular load.
Still a further object of this invention is to provide a new and improved hydraulic brake control assembly which is simple in construction and inexpensive in manufacturing cost, while providing a reliable and proper hydraulic braking pressure to the rear and front wheels.
Additional objects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.
To achieve the foregoing objects and in accordance with the purpose of the invention, as embodied and broadly described herein, an improved hydraulic brake control assembly for automotive vehicles having front and rear wheel brake means and a hydraulic braking master cylinder fluidically connected to each of the front and rear brake means is provided comprising: (1) valve proportioning means interposed between the master cylinder and at least one of the wheel brake means for regulating the hydraulic pressure applied to at least one of the wheel brake means from the master cylinder in accordance with vehicular load, wherein the valve proportioning means includes a reciprocable proportioning piston subjected at a first section formed in said valve proportioning means to the hydraulic pressure in the wheel brake means and at a second section formed in the valve proportioning means to the hydraulic pressure from the master cylinder, the proportioning piston being normally urged to a position allowing hydraulic pressure communication between the first and second sections; (2) control means responsive to vehicular deceleration and hydraulic pressure from the master cylinder for controlling the valve proportioning means in accordance with vehicular load wherein the control means includes -- (a) slidable piston means engaged with said reciprocable proportioning piston varied in response to hydraulic pressure applied to the piston means, the piston means normally urging the proportioning piston to an open hydraulic pressure communication position; (b) first passage means for supplying hydraulic pressure from the master cylinder to the piston means; (c) first valve means interposed in the first passage means for controlling admission of the hydraulic pressure supplied to the piston means in response to vehicular deceleration; (d) orifice means interposed in the passage means for throttling the hydraulic pressure supplied to the piston control means; and (e) second valve means positioned parallel to the orifice means in the passage means and normally closed, the second valve means being opened when a predetermined difference in hydraulic pressure is reached on opposite sides of the orifice means for supplying the hydraulic pressure to the piston means without pressure throttling by the orifice means.
It is preferred in one embodiment of the invention that the second valve means be a relief valve and wherein the orifice means and relief valve are positioned in the first passage means between the first valve means and the slidable piston means.
It is preferred in another embodiment of the invention that the second valve means be a metering valve and wherein the first valve means is positioned in the first passage means between the combination of the orifice means and metering valve, and the slidable piston means.
It is preferred in both embodiments of the invention that a third valve means be provided in the first passage means normally urged closed for preventing supply of hydraulic pressure to the slidable piston means and opened in response to a predetermined hydraulic pressure for admitting the hydraulic pressure to the slidable piston means.
It is further preferred that the at least one wheel brake means be the rear wheel brake means and that the front wheel brake means be directly connected to the hydraulic braking master cylinder.
Finally, it is preferred in both embodiments of the invention that the slidable piston means comprise a slidable piston mounted in a housing co-axially with the reciprocal proportioning piston with a spring positioned between opposing ends of the slidable piston and the proportioning piston for normally urging the proportioning piston to an open hydraulic pressure position, and wherein a first pressure control chamber is formed in the first passage means at the other end of the slidable piston for moving the slidable piston to vary the urging force of the spring exerted on the reciprocal proportioning piston in response to hydraulic pressure supplied to the first pressure control chamber.